Thermally and magnetically responsive electrical control device



Nov. 14, 1967 E. GAUTHIER 3,353,123

THERMALLY AND MAGNETICALLY RESPONSIVE ELECTRICAL CONTROL DEVICE Filed Feb. 17, 1966 2 Sheets-Sheet 1 I INVENTOR. 6502s: 5. 6407/1/16? G. E. GAUTHIER Nov. 14, 1967 I THERMALLY AND MAGNETICALLY RESPONSIVE ELECTRICAL CONTROL DEVICE 1 2 Sheets-Sheet 2 Filed Feb. l7, 1966 FIG/3c [/Vl/E/VTOH 6644 66 [64077002 i ATTORNEY United States Patent 3,353,128 THERMALLY AND MAGNETICALLY RESPON- SIVE ELECTRlCAL CONTROL DEVICE George E. Gauthier, Plainville, C0nn., assignor to General Electric Company, a corporation of New York Filed Feb. 17, 1966, Ser. No. 528,276 Claims. (Cl. 335-35) ABSTRACT OF THE DESCLOSURE An electric circuit breaker of the latch trip type, including a first bimetallic strip which is heated by heat generated in a short-circuited secondary winding electromagnetically coupled to a conductor in a controlled circuit and a second bimetallic strip heated by heat generated in the primary conductor itself; the second bimetallic strip acts on a movable magnetic armature to initiate movement of the armature toward a pair of magnetic pole portions of a magnetic field piece energized by flux associated with the current flowing in the primary conductor.

The present invention relates to electrical control devices, and more particularly, to a circuit breaker having a movable contact operated between open and closed positions by an operating mechanism which includes a releasable member releasable to cause automatic opening of the contacts by both thermally and magnetically responsive means to interrupt the circuit passing therethrough upon predetermined overload conditions therein.

In some circuit breakers, it is desirable to provide thermal and magnetic response by having magnetically operable means actuated upon the occurrence of a predetermine relatively high overload current and thermally responsive means actuated upon the occurrence of predetermined relatively low overload currents. In some applications, a transformer-type thermally responsive means is utilized for heating a bimetallic strip which is actuated upon the occurrence of continuous, relatively low overload currents. Such a transformer-type device is disclosed in copending United States patent application Ser. No. 423,942 of George E. Gauthier, filed Jan. 7, 1965, and assigned to the same assignee as the present invention, now abandoned.

Although the various prior art devices such as that shown in the aforementioned United States patent ap plication protect the associated circuits only upon the occurrence of relatively high overload current and upon the occurrence of continuous, relatively low overload currents, generally these devices do not provide for protection of the circuit upon the occurrence of a sudden, intermediate overload current which is insuificient to actuate the magnetically operable means but is sufficiently high to cause damage to the associated apparatus. More particularly, since only small amounts of heat are generated by small overload currents, the thermally responsive means used to trip the circuit under these conditions must be adapted to be sensitive to continuous small overload currents and yet not cause tripping of the circuit during minor current fluctuations. Accordingly, such thermally responsive means are inherently slow acting to avoid unnecessary tripping of the circuit breaker and are generally ineffective to prevent damage to the circuit by sudden intermediate overload currents.

It is an object of the present invention to provide a thermally and magnetically responsive electrical control device which is responsive to relatively low, intermediate and relatively high overload conditions in an electric circuit.

Another object is to provide such a thermally and magnetically responsive electrical control device providing two independent thermally responsive means for actuation at predetermined low and intermediate overload currents and a magnetically responsive device for actuation by a relatively high overload current.

Still another object is to provide such a control device utilizing a transformer-type thermally responsive means to provide sensitivity to continuous, low overload currents.

It has now been found that the foregoing objects and other advantages can readily be attained in a thermally and magnetically responsive electrical control device for use in an electrical circuit by providing a support with an electrical conductor mounted thereon and a control member movable thereon to perform control functions. A magnetic field piece mounted on the support in close proximity to the conductor forms a path for the magnetic flux created by an electrical current passing through the electrical conductor and has a pair of spaced arm portions each providing a pole portion, one of the arm portions being adapted to be saturated by the magnetic flux before the other arm portion. An armature movably mounted on the support is normally magnetically attracted toward engagement with the first mentioned arm portion but is also movable by magnetic attraction toward engagement with the other arm portion upon the occurrence of a relatively large overload current in the conductor causing saturation of the flux path provided by the first mentioned arm portion. Movement of the armature toward the other arm portion produces engagement with the control member to cause movement thereof.

An intermediate overload current thermally responsive means mounted on the support is responsive to current carried by the conductor and is operable upon the occurrence of a predetermined inter-mediate overload current to move the armature away from the first mentioned arm portion and toward the other arm portion to permit the magnetic field of the other arm portion to draw the armature into engagement therewith and into engagement with the control member to cause movement thereof. A low overload current thermally responsive means mounted on the support is also responsive to current carried by the conductor and is operable upon the occurrence of a predetermined relatively low overload current to engage the control member for causing movement thereof.

One of the intermediate and low overload current thermally responsive means is adapted to be relatively slow acting to prevent actuation by minor current fluctuations but it is sensitive to small or relatively low continuous overload currents so that it wil be actuated by the continuance of the overload current.

The other thermally responsive means must be adapted to be fast acting upon the occurrence of an intermediate overload circuit to prevent damage to the circuit. It is advantageously a bimetallic strip mounted on the conductor which is adapted to be actuated upon the occurrence of sudden, intermediate overload currents which would cause damage to the circuit before the slower acting thermally responsive means could be actuated and which are insutficientto actuate the magnetically responsive means.

The intermediate overload current responsive means may be of the transformer type having a magnetic core member mounted on the support in close proximity to the conductor to form a path for the magnetic flux created by an electrical current passing through the conductor. A secondary winding is mounted on the core member and is energizable by the flux therein, and a bimetallic strip is mounted in thermal contact with the secondary winding and is engageable with the control member to effect movement thereof. This transformer type of thermally responsive electrical control devices is slow acting because heating of the secondary winding must occur before the bimetallic strip is actuated. Accordingly, it is effective for actuation by continuous, relatively low overload currents, but it is normally ineffective to protect a circuit from sudden intermediate overload currents because of its slow operation.

The intermediate overload current thermally responsive means and the magnetically responsive means engage and move the armature upon actuation by an overload current to effect operation of the control device. In the preferred embodiment, the armature and the second thermally responsive means are adapted to engage a tripping bar upon actuation thereof and movement thereof in turn actuates the tripping mechanism of an associated circuit breaker.

The electrical control device desirably includes biasing means mounted on the support for biasing the armature toward the first mentioned arm portion of the mag netic field piece to hold the armature in its normal on tion of the magnetic field piece.

When a large overload current occurs, the flux path provided by the first mentioned arm portion becomes saturated before the other arm portion which subsequently provides sufiiciently greater magnetic attraction to pull the armature against the restraining force of the spring and the magnetic attraction of the first mentioned arm portion. When an intermediate overload current occurs, the second thermally responsive means overcomes the restraining force of the spring and the magnetic attraction of the first mentioned arm portion to move the armature away from the first mentioned arm portion so that the armature is magnetically attracted and pulled toward the other arm portion for actuation of the control member.

Additional objects and aspects of the invention will be pointed out in the following detailed description and illustrated in the accompanying drawings and the scope will be particularly pointed out in the appended claims.

In the drawings: FIGURE 1 is a side elevational view of a multipole circuit breaker with a portion of the operating parts therein enlarged scale of a portion of the operating parts of the circuit breaker of FIGURE 1.

Referring now in detail to the attached drawings, a multipole circuit breaker embodying the present invention is generally designated by the numeral 10. .In accordance with conventional construction, the circuit, breaker 10 has a housing 12 and a manually operable handle 14 which is connected through an appropriate operating mechanism generally designated by the numeral 16 to position a pair of movable electrical contacts 18 and 20' in open and closed positions. The operating mechanism 16 includes a latch member 22 adapted to be secured in a latched position by a tripping mechanism generally designated by the numeral 24 which may be actuated for automatic interruption of the current flow in the main conductors of the circuit breaker under overload conditions in response to a thermal or a magnetic tripping as will be explained more fully hereinafter.

The type of operating mechanism 16 suitable for use with the present invention is desirably similar to that described in United States Letters Patent No. 2,921,169, issued to E. B. Judd et al. on I an. 12, 1960, and assigned to the same assignee as the present invention; The type of linkage or trip mechanism 24 suitable for use with the present invention is disclosed in United States Letters Patent No. 2,884,497, issued to H. M. Steven et al. on Apr..29, 1959, and assigned to the same assignee as the present invention. a

In FIGURE 1 the movable contacts 18 and 20 of the circuit breaker 10 are illustrated in the on position wherein they contact a pair of stationary contacts 26 and 28 Whichare supported on the conductor 30. The movable contacts 18 and 20 are mounted on the contact arm 32 which is pivotably supported on; the housing 12 and is electrically connected to the flexible conductor 34. Electrically connected to the contact arm 32 are the conductor strap 36 and another conductor 38 which passes through an aperture in a tripping assembly generally designated by the numeral 40 and enclosed with a housing comprising two mating molded parts 42 and 44. The housing base 42 is the larger of the two and serves as a support for parts of the trip mechanism 24 while the part 44 serves as a cover. The tripunit 44) is responsive to the flow of overload currentin the main conductor 30 to release the latch member 22 which causes the operating mechanism 16 to actuate the contact arm 32 and the movable contacts 18 and 20 ,of the circuit breaker 10 to interrupt the flow of overload current.

The circuit breaker 10 is of the multipole type wherein the housing 12 has a plurality of pole chambers and a plurality of movable contacts 18 and 20 in each of the pole chambers. The operating mechanism 16 may be operated by manual movement of the handle 14 so that movable contacts 18 and 20 of each single pole chamber may be positioned in the on position wherein they are engaged with the stationary contacts 26 and 28 or the handle 14 may be positioned in the off position, disengaging the movable contactsil8 and 26 in each pole chamber from .the stationary contacts 26 and 28 and interrupting the flow of current therethrough. The movable contacts 18 and 20 may also be disengaged from the stationary contacts 26 and 28 by automatic release of the latch member 22 by the trip mechanism 24 in response to actuation by thermally sensitive or magnetically operable devices in the trip unit 40.

Referring now to FIGURE 2, there is shown in detail the operating parts wherein the latch member 22 is in its latched position corresponding to the on position of the circuit breaker 10 as is illustrated in FIGURE -1. The trip bar 46 is pivotally supported on the housing base 42 by a pivot pin 48 so as to be engageable with a low thermally responsive bimetallic strip 50 through an adjusting screw 52. Also supported on the pivot pin 48 is an armature 54 which is positioned to be engageable by an adjusting screw 56 on an intermediate overload current thermally responsive bimetallic strip 57 which is mounted on the conductor 38.

The conductor 38 passes through an assembly which comprises an insulating member 58 having laminated magnetic core members 60 mounted thereon. The insulating member 58 is configured to be received and supported in the trip unit 40 and has a plurality of apertures (not shown) for passage of the primary conductors of the multipole circuit breaker such as the conductor 38 which conductors are bolted to the housing by suitable fasteners 62.

The insulating member 58 also supports a secondary winding 64 mounted on each core member 60. The secondary winding 64 is preferably of the single turn, shortcircuited type and may typically comprise a single loop of solid copper, as illustrated. The low overload current thermally responsive bimetallic strip 50 is fixedly attached to the secondary winding 64.

To provide a magnetically operable tripping means a main pair of magnetic pole extensions 66- of relatively large volume is mounted on the insulating member 58 opposite each magnetic core member 60 and the extensions 66 are spaced apart to define an air gap which is magnetically in parallel with its associated magnetic core member 60. A pair of auxiliary magnetic pole extensions or back drag poles 68 of relatively small volume are mounted on the main pair of pole extensions 66 and have end portions extending in parallel spaced relationship with the end portions of the main pole extensions 66. In this manner, the main pair of magnetic pole extensions 66 and the auxiliary pair of magnetic pole extensions 68 form spaced apart arm or pole portions which are positioned to form spaced arm portions, each magnetically engageable with the armature 54.

The armature 54 is fabricated from a magnetically susceptible material and is of suflicient length so that its free end portion extends between the parallel end portions of the pairs of pole extensions 66, 68 so that it may be magnetically engaged by the end portions of either pair. The trip bar 46 is biased in a counterclockwise direction as viewed in FIGURE 2 by a helical tension spring 70 supported at one of its ends on the housing base 42 of the trip unit 40. The spring 70 holds the armature 54 in its normal on position in engagement with the auxiliary pair of magnetic pole extensions when no current is flowing in the conductor.

Current passing through the primary conductor 38 creates a magnetic field which courses through the magnetic core member 60, the main magnetic pole extensions 66 and the back-drag or auxiliary magnetic pole extensions 68. Since the armature 54 is within the parallel magnetic flux path through the extensions 66, 68, the flow of normal current produces a magnetic flux which tends to hold the armature 54 in cooperation with spring 70 in the illustrated on position against the auxiliary magnetic pole extensions 68 and in engagement with the adjusting screw 56 on the intermediate overload current bimetallic strip 57. Upon the occurrence of predetermined high overload current conditions, the auxiliary magnetic poles 68 become magnetically saturated and greater magnetic attraction is generated within the larger magnetic pole portions 66 so that, as viewed in FIGURE 2, the armature 54 is pulled to the left into engagement with the larger magnetic pole portions 66 against the force of spring 70 and the magnetic force of the auxiliary magnetic poles 68. During this movement, the armature 54 displaces the trip bar 46 to depress the toggle linkage of the tripping mechanism 24 which allows the spring loaded latch member 22 to escape from its latched position so that the operating mechanism 16 rapidly disengages the movable contacts 18 and 20 from the stationary contacts 26 and 28.

The bimetallic strip is similarly responsive to the flow of excessive overload current conditions in the primary conductor 38. Such an overload current generates an increase .in the magnetic field in the magnetic core member and the single turn short-circuited secondary winding 64. Because the secondary winding 64 is short-circuited and a very good electrical conductor such as copper, for instance, very high eddy currents are generated in the secondary winding which quickly heat the metal of the secondary winding 64. This heat is rapidly conducted to the thermally responsive bimetallic strip 50 which is in direct contact therewith. Since the bimetallic strip 50 is constructed, arranged and positioned to deflect to the right as viewed in FIGURE 2, its bending causes the calibrating screw 52 to engage the trip bar 46 and to displace it in a clockwise direction and actuate the tripping mechanism 24. Thus, this strip 50 is responsive to a relatively small continuous overload current by proper adjustment of the calibrating screw 52. t

A more rapid acting combined thermal and magnetic type of tripping is provided by the bimetallic strip 57 which is mounted directly on the conductor 38 and is adapted to be actuated by a sudden intermediate overload current which causes rapid heating of the conductor 38 but which is not large enough to cause the armature 54 to be pulled from engagement with the auxiliary magnetic pole extensions 68. When the bimetallic strip 57 is actuated by a sudden increase in the temperature of the conductor 38 caused by a predetermined intermediate overload current passing therethrough, the bimetallic strip 57 bends to the left as viewed in FIGURE 2 and the adjusting screw 56 forces the armature 54 away from engagement with the back-drag pole 68 whereupon the armature 54 is pulled magnetically toward the magnetic poles 66. As the armature 54 rotates, it engages the trip bar 46 which operates the trip mechanism 24 releasing the latch member 22 and causes the circuit breaker to move to the open position.

Thus, in operation of the present invention, the magnetic core member 66, secondary winding 64, and bimetallic strip 50 cooperate to move the trip bar 46 upon the occurrence of a relatively low but continuous overload current. The main and auxiliary magnetic pole extensions 66 and 68 rapidly respond upon the occurrence of a relatively large sudden overload current independently of the bimetallic strip 50 causing the armature 54 to rotate the trip bar 46. The bimetallic strip 57 is adapted to be actuated by an intermediate overload current which is insuflicient to cause magnetic actuation of the armature 54 but is large enough to damage the circuit before tripping would occur by the action of the slower responding first bimetallic strip 50. The intermediate overload current bimetallic strip 57 is adjusted so that it will not be actuated by the low continuous overload current that is sufiicient to operate the low overload current bimetallic strip 50'. Thus, the device is adapted to be responsive to various overload currents and to effectively trip the circuit breaker mechanism before any damage occurs to the elements of the circuit.

Accordingly, the present invention provides a thermally and magnetically responsive electrical control device which is responsive to relatively low, intermediate and relatively high overload circuit conditions. Two independent thermally responsive means are provided for actuating the control device at predetermined low and intermediate overload currents and, in addition, a magnetically responsive device is provided for actuating a control device at relatively high overload currents. Accordingly, a novel, thermally and magnetically responsive electrical control device is provided which will protect the elements of a circuit from damage under all possible overload conditions.

While the invention has been shown in one specific preferred embodiment it will be readily apparent that many modifications thereof may be made without departing from the spirit of the invention. It is therefore intended by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a thermally and magnetically responsive electrical control device for use in an electrical circuit, the combination comprising:

(a) a support;

(b) an electrical conductor mounted on said support;

(c) a control member mounted on said support and movable to perform a control function;

(d) a magnetic field piece mounted on said support in close proximity to said conductor forming a path of the magnetic flux created by an electrical current passing through said electrical conductor, said magnetic field piece having a pair of spaced arm portions each providing a pole portion, one of said arm portions being adapted to be saturated by the magnetic flux before the other of said arm portions;

sesame (e) a movable armature mounted on said support and normally magnetically attracted toward engagement with said one arm portion, said armature being movable by magnetic attraction of said other arm portion toward engagement with said other arm por-' tion upon the occurrence of a relatively large overload current in said conductor causing saturation of the flux path provided by said one arm portion, said armature being engageable with said control member upon magnetic engagement by said other arm portion to cause movement thereof; I r

(f) intermediate overload current thermally responsive means mounted on said support and responsive to current carried by said conductor, said intermediate overload current thermally responsive means being operable upon the occurrence of a predetermined overload current to move said armature away from said one arm portion and toward said other arm portion to permit said other arm portion to move said armature by magnetic attraction into engagement therewith and into engagement with said control member to cause movement thereof; and

(g) low overload current thermally responsive means mounted on said support and responsive to current carried by said conductor, said low overload current thermally responsive means being operable upon the occurrence of a predetermined relatively low overload current to engage said control member and effect movement thereof;

2. The thermally and magnetically responsive electrical control device of claim 1 wherein said intermediate overload current thermally responsive means is a bimetallic strip mounted on said conductor and engageable with said armature to effect movement upon bending thereof.

3. The thermally and magnetically responsiveelectrical control device of claim 1 wherein said low overload current thermally responsive means includes a magnetic core member mounted on said support in close proximity .to said conductor and forming a path for the magnetic flux created by an electrical current passing through said conductor, a secondary winding mounted on said core memher and energizable by flux in said magnetic core member, and a bimetallic strip mounted in thermal contact with said secondary winding, said bimetallic strip being engageable with said control member to effect movement thereof upon bending due to differential thermal expansion.

4. The thermally and magnetically responsive electrical control device of claim 1 wherein said control member is a trip bar pivoted on said housing and pivotable by movement of said armature and by bending of said low overload current thermally responsive means to actuate the tripping mechanism of an associated circuit breaker.

5. An electrical circuit breaker comprising:

(a) arsupport;

(b) a movable and a stationary contact mounted on said support;

() an operating mechanism mounted on said support for operating said movable contact between open and closed circuit positions, said operating mechanism including a releasable member adapted to cause automatic opening of said contacts upon release thereof;

(d) a tripping mechanism mounted on said support and engaged with said releasable member for releasing said releasable member upon actuation of said tripping mechanism;

(e) an electrical conductor mounted on said support;

(f) a magnetic field piece mounted on said support in close proximity to said conductor forming a path for the magnetic flux created .by an electrical current passing through said electrical conductor, said magnetic field piece having a pair of spaced arm portions each providing a pole portion, one of said arm 3 r portions being adapted to be saturated by the magnetic flux before the other of said arm portions;

(g) a movable armature mounted on said support and normally magnetically attracted toward engagement with said one arm portion, said armature being movable by magnetic attraction of said other arm portion toward engagement with said other arm portion upon the occurrence of a relatively large overload currentin said conductor causing saturation of the flux path provided by said one arm portion, said armature being engageable with said tripping mechanism upon engagement by said other arm portion to cause actuation thereof;

(h) intermediate overload current thermally responsive means mounted on said support and responsive to current carried by said conductor, said intermediate overload current thermally responsive means being operable upon the occurrence of a predetermined intermediate overload current to move said armature away from said one arm portion and to- Ward said other arm portion to permit said other armportion to move said armature by magnetic attraction into engagement therewith and into engagement with said tripping mechanism to cause actuation thereof; and

(i) low overload current thermally responsive means mounted on said support and responsive to current carried by said conductor, said lowoverload current thermaily responsive means being operable upon the occurrence of a predetermined relatively low overload current to engage said tripping mechanism and effect actuation thereof.

6. The electrical circuit breaker of claim 5 wherein said intermediate overload current thermally responsive means is a bimetallic strip mounted on said conductor and engageable with said armature to effect movement upon bendingthereof and wherein said low overload current thermally responsive means includes a magnetic core member mounted on said support in close proximity to said conductor and forming a path for the magnetic flux created by an electrical current passing through said conductor, a secondary winding mounted on said core member and energizable by flux in said magnetic core member, and a bimetallic strip mounted in thermal contact with said secondary winding, said bimetallic strip being engageable with said control member to effect movement thereof upon bending due to ditferential thermal expansion.

7. In a thermally and magnetically responsive electrical control device for use in an electrical circuit, the combination comprising:

(a) a support;

(b) an electrical conductor mounted on said support;

(0) a control member mounted on said support and movable to perform a control function;

(d) a first magnetic field piece mounted on said support in close proximity to said conductor and forming a path for the magnetic flux created by electrical current passing through said electrical conductor;

(e) a short-circuited secondary winding on said first magneticiield piece;

( f) a first bimetallic strip mounted in thermal contact with said secondary Winding and engageable with said control member to effect movement thereof upon bending of said first bimetallic strip due to dif ferential thermal expansion upon the occurrenceof predetermined low overload current conditions;

.(g) a second magnetic field piece mounted on said support and having a'pair of spaced arm portions each providing a pole portion;

(h) arnovable armature mounted on said support;

(i) means biasing said movable armature to a position spaced away from 'said pole portions of said second magnetic field piece, said armature being movable directly by magnetic attraction toward said pole portions upon the occurrence of predetermined high overload current conditions, said armature engaging said control member upon movement toward said pole portions to also effect movement thereof;

(j) a second bimetallic strip supported on said support and responsive to heat generated by current carried by said electrical conductor;

(k) means carried by said second bimetallic strip for engaging said movable armature to initiate movement of said armature toward said pole portions upon the occurrence of predetermined intermediate overload current conditions greater than said low overload current conditions actuating said first bemetallic strip and less than said high overload current conditions actuating said magnetic armature.

8. An electric circuit breaker as set forth in claim 7 wherein said second magnetic field piece includes a second pair of pole portions in juxtaposed relation to said first pair of pole portions, said biasing means normally biasing said armature into engagement with said second pair of pole portions, and said second bimetalli strip acting on said armature to move said armature away from engagement with said second pair of pole portions.

9. In a thermally and magnetically responsive electrical control device for use in an electrical circuit, the combination comprising:

(a) a support;

(b) an electrical conductor mounted on said support;

() a control member mounted on said support and movable to perform a control function;

(d) a magnetic field piece mounted on said support in close proximity to said conductor forming a path for the magnetic flux created by an electrical current passing through said electrical conductor, said magnetic field piece having a pair of spaced arm portions each providing a pole portion, one of said arm portions being adapted to be saturated by the magnetic flux before the other of said arm portions;

(e) a movable armature mounted on said support and normally magnetically attracted toward engagement with said one arm portion, said armature being movable by magnetic attraction of said other arm portion toward engagement with said other arm portion upon the occurrence of a relatively large overload current in said conductor causing saturation of the flux path provided by said one arm portion, said armature being engageable with said control member upon magnetic engagement by said other arm portion to cause movement thereof;

(f) biasing means mounted on said support and biasing said armature toward engagement with said one arm portion, said biasing means providing additional force to be overcome by the magnetic attraction of said other arm portion before said armature is movable toward engagement therewith; overload current responsive means mounted on said support to move said armature away from said one arm portion and toward said other arm portion to permit said other arm portion to move said armature by magnetic attraction into engagement therewith and into engagement with said control member to cause movement thereof;

(g) second thermally responsive means mounted on said support and responsive to current carried by said conductor, said second thermally responsive means being operable upon the occurrence of a predetermined relatively low overload current to engage said control member and effect movement thereof; and

(h) said intermediate overload current responsive means comprising a bimetallic strip mounted on said conductor and engageable with said armature to effect movement upon bending thereof and said low overload current thermally responsive means comprising a magnetic core member mounted on said support in close proximity to said conductor and forming a path for the magnetic flux created by an electrical current passing through said conductor, a secondary winding mounted on said core member and energizable by flux in said magnetic core member, and a bimetallic strip mounted in thermal con tact with said secondary winding, said bimetallic strip being engageable with said control member to effect movement thereof upon bending due to differential thermal expansion.

10. In a thermally and magnetically responsive electrical control device for use in an electrical circuit, the combination comprising:

(a) a support;

(b) an electrical conductor mounted on said support;

(0) a control member mounted on said support and movable to perform a control function;

((1) a magnetic field piece mounted on said support in close proximity to said conductor forming a path for the magnetic flux created by an electrical current passing through said electrical conductor, said magnetic field piece having a pair of spaced arm portions each providing a pole portion, one of said arm portions being adapted to be saturated by the magnetic flux before the other of said arm portions;

(e) a movable armature mounted on said support and normally magnetically attracted toward engagement with said one arm portion, said armature being movable by magnetic attraction of said other arm portion toward engagement with said other arm portion upon the occurrence of a relatively large overload current in said conductor causing saturation of the flux path provided by said one arm portion, said armature being engageable with said control member upon magnetic engagement by said other arm portion to cause movement thereof;

(f) biasing means mounted on said support and biasing said armature toward engagement with said one arm portion, said biasing means providing additional force to be overcome by the magnetic attraction of said other arm portion before said armature is movable toward engagement therewith; overload current responsive means mounted on said support to move said armature away from said one arm portion and toward said other arm portion to permit said other arm portion to move said armature by magnetic attraction into engagement therewith and into engagement with said control member to cause movement thereof;

(g) second thermally responsive means mounted on said support and responsive to current carried by said conductor, said second thermally responsive means being operable upon the occurrence of a predetermined relatively low overload current to engage said control member and effect movement thereof; and

(h) said control member comprising a trip bar pivoted on said housing and pivotable by movement of said armature and by bending of said low overload thermally responsive means to actuate the tripping mechanism of an associated circuit breaker.

References Cited UNITED STATES PATENTS 2,981,811 4/196-1 Stevens et al 335-35 BERNARD A. GILHEANY, Primary Examiner. H. BROOME, Assistant Examiner. 

1. IN A THERMALLY AND MAGNETICALLY RESPONSIVE ELECTRICAL CONTROL DEVICE FOR USE IN AN ELECTRICAL CIRCUIT, THE COMBINATION COMPRISING: (A) A SUPPORT; (B) AN ELECTRICAL CONDUCTOR MOUNTED ON SAID SUPPORT; (C) A CONTROL MEMBER MOUNTED ON SAID SUPPORT AND MOVABLE TO PERFORM A CONTROL FUNCTION; (D) A MAGNETIC FIELD PIECE MOUNTED ON SAID SUPPORT IN CLOSE PROXIMITY TO SAID CONDUCTOR FORMING A PATH OF THE MAGNETIC FLUX CREATED BY AN ELECTRICAL CURRENT PASSING THROUGH SAID ELECTRICAL CONDUCTOR, SAID MAGNETIC FIELD PIECE HAVING A PAIR OF SPACED ARM PORTIONS EACH PROVIDING A POLE PORTION, ONE OF SAID ARM PORTIONS BEING ADAPTED TO BE SATURATED BY THE MAGNETIC FLUX BEFORE THE OTHER OF SAID ARM PORTIONS; (E) A MOVABLE ARMATURE MOUNTED ON SAID SUPPORT AND NORMALLY MAGNETICALLY ATTRACTED TOWARD ENGAGEMENT WITH SAID ONE ARM PORTION, SAID ARMATURE BEING MOVABLE BY MAGNETIC ATTRACTION OF SAID OTHER ARM PORTION TOWARD ENGAGEMENT WITH SAID OTHER ARM PORTION UPON THE OCCURRENCE OF A RELATIVELY LARGE OVERLOAD CURRENT IN SAID CONDUCTOR CAUSING SATURATION OF THE FLUX PATH PROVIDED BY SAID ONE ARM PORTION, SAID ARMATURE BEING ENGAGEABLE WITH SAID CONTROL MEMBER UPON MAGNETIC ENGAGEMENT BY SAID OTHER ARM PORTION TO CAUSE MOVEMENT THEREOF; (F) INTERMEDIATE OVERLOAD CURRENT THERMALLY RESPONSIVE MEANS MOUNTED ON SAID SUPPORT AND RESPONSIVE TO CURRENT CARRIED BY SAID CONDUCTOR, SAID INTERMEDIATE OVERLOAD CURRENT THERMALLY RESPONSIVE MEANS BEING OPERABLE UPON THE ACCURRENCE OF A PREDETERMINED OVERLOAD CURRENT TO MOVE SAID ARMATURE AWAY FROM SAID ONE ARM PORTION AND TOWARD SAID OTHER ARM PORTION TO PERMIT SAID OTHER ARM PORTION TO MOVE SAID ARMATURE BY MAGNETIC ATTRACTION INTO ENGAGEMENT THEREWITH AND INTO ENGAGEMENT WITH SAID CONTROL MEMBER TO CAUSE MOVEMENT THEREOF; AND (G) LOW OVERLOAD CURRENT THERMALLY RESPONSIVE MEANS MOUNTED ON SAID SUPPORT AND RESPONSIVE TO CURRENT CARRIED BY SAID CONDUCTOR, SAID LOW OVERLOAD CURRENT THERMALLY RESPONSIVE MEANS BEING OPERABLE UPON THE OCCURRENCE OF A PREDETERMINED RELATIVELY LOW OVERLOAD CURRENT TO ENGAGE SAID CONTROL MEMBER AND EFFECT MOVEMENT THEREOF. 